IE980585A1 - A process for manufacturing a printing ink - Google Patents

Abstract

An ink manufacturing process of the invention facilitates the rapid production of alarge number of relatively small batches of different coloured inks. A set of base inks are prepared comprising a plurality of different coloured inks forming a spectrum of desired base solours. The base inks do not include a drying agent so they will not set. To produce a printing ink of a desired colour, selected quantities of two or more different coloured base inks are mixed together with a drying agent.

Description

A Process for Manufacturing a Printing Ink This invention relates to a process for manufacturing a printing ink.

The invention is particularly concerned with the production of high quality printing inks in an efficient and trouble-free manner.

It is an object of the invention to provide a process which facilitates the rapid production of a large number of relatively small batches of different coloured inks.

According to the invention there is provided a process for manufacturing a printing ink, comprising the steps: preparing selected powder pigments, taking a sample of each pigment, mixing said sample with a silicone wetting agent for forming a slurry, filtering the slurry, measuring the conductivity of the slurry for establishing the potassium chloride content of the pigment as an expression of the total salt content of the pigment, controlling the salt content of the pigment to a preset desirable range, weighing out a pre-desired amount of one or more of the selected powder pigments, delivering each selected powder pigment to a mixer, preparing a resin, weighing out a pre-desired quantity of resin, delivering the resin to the mixer, mixing the pigment with the resin in the mixer for a pre-desired time period for dispersing the pigment throughout the resin, forming an ink paste, INT CL - 2 delivering the ink paste to a mill, passing the ink paste through the mill, grinding the pigment into the resin in the mill for producing an homogenous ink paste of a desired viscosity and reducing the pigment particles within the paste to a preset desirable size, combining selected additive materials with the paste for conditioning the paste and producing a printing ink of preset desirable characteristics .

In a preferred embodiment of the invention the process includes; preparing a set of base inks comprising a plurality of different coloured inks of a desired viscosity forming a spectrum of desired base ink colours, delivering each base ink to an associated holding tank, preparing a formulation for printing ink of a desired colour for forming a quantity of ink of the desired colour by combining two or more predetermined quantities of selected base inks of different colour, weighing a pre-desired amount of each selected base ink according to the formulation, delivering the selected base inks to a mixing tray, adding a preset amount of a drying agent to the mixing tray, mixing the selected base inks and the drying agent in the mixing tray for forming the printing ink of the desired colour, - 3 delivering the coloured ink to a container.

In a particularly preferred embodiment the process includes the step of preparing the resin by combining preset amounts of two or more selected resins including a gel resin, controlling the amount of gel resin for controlling the viscosity of the ink to a preset desirable value.

Preferably the gel resin comprises between 30% and 60% by weight of the total resin.

In another embodiment the process includes the step of controlling the pH of the printing ink to a pH of between 8.5 and 9.5.

In a further embodiment the resin is a polyester resin and one of the additive materials comprises a cross-linking agent associated with the resin, the quantities of the resin and the cross-linking agent being in the ratio of 3:1 by weight in the ink.

The invention will be more clearly understood from the following description of some embodiments thereof with reference to the accompanying drawing which is a schematic representation of a process for manufacturing a printing ink according to the invention.

Samples of selected powder pigments are delivered to a testing station 10. Each sample is mixed with a silicone wetting agent for forming a slurry. The slurry is then passed through a filter into a collecting cup. The conductivity of the slurry in the collecting cup is then measured for establishing the potassium chloride content of the pigment as an expression of the total salt content of the pigment. The salt content of the pigment is - 4 controlled to a preset desirable range. Acceptable pigments are held in pigment storage containers 12.

A pre-desired amount of one or more selected pigments corresponding to a desired ink colour are delivered from associated storage containers 12 to a weigher. The selected pigments are weighed and delivered to a mixer 16. A resin is prepared and a pre-desired quantity of resin is delivered from a resin storage tank 18, weighed and delivered to the mixer 16.

The mixer is operated to mix the pigment with the resin for dispersing the pigment throughout the resin, forming an ink paste.

The ink paste is delivered to a mill 20 downstream of the mixer 16 and passed through the mill 20. Within the mill 20 the pigment is ground into the resin, producing an homogenous ink paste of the desired colour while reducing the pigment particles within the paste to a preset desirable size, preferably not exceeding 2 microns.

Various additives such as drying agents and anti-oxidants may then be added to the ink paste in the mill for conditioning the ink paste and producing a printing ink of preset desirable characteristics.

Optionally also an anti-oxidant such as hydroquinone or methylethylhetoxy can also be added to the mill 20. The amount of anti-oxidant will depend on the particular coloured inks being combined. For example for yellow colours the anti-oxidant might comprise 1.2 - 1.4% whereas with the black colours only in the order of 0.8% antioxidant may be used. - 5 The printing ink is discharged from the mill 20 into a storage container 22.

In an alternative arrangement a plurality of different coloured printing inks of a desired viscosity are prepared forming a set of base inks, typically of about ten different colours. Each of the base inks does not include a drying agent so that it will not set. Each base ink is delivered from the mill 20 to an associated holding tank 24. Typically ten base inks of different colours are produced and delivered to the holding tanks 24.

The viscosity of the base inks is controlled such that it can be manually mixed. The viscosity is controlled by including a gel resin as part of the resin in the ink. Typically the gel resin will comprise between 30% and 60% by weight of the total resin content of the ink, the total resin content being in the order of 70% by weight of the printing ink.

A formulation is prepared for producing printing ink of a desired colour by combining two or more predetermined quantities of selected base inks of different colour.

Selected amounts of two or more of the base inks are weighed on a weigher 26 and delivered to a mixing tray 28. To the mixing tray are also added a drying agent such as 10% cobalt solution and/or a 10% manganese solution. In an alternative arrangement a mixture of cobalt and zirconium could be used as the drying agent.

The selected base inks and drying agent are manually mixed with a stirrer in the mixing tray and then packaged in containers. - 6 It will be appreciated that the production of a set of base inks as described enables a wide range of different coloured inks to be produced rapidly on demand. It is particularly important where a large number of relatively small batches or quantities such as 20 to 100 kilograms of ink are being produced.

In another embodiment the resin comprises a polyester resin and one of the additive materials comprises a crosslinking agent associated with the polyester resin.

Ideally, the polyester resin and cross-linking agent are mixed in the ink in the ratio 3:1.

Advantageously, also according to the invention the pH of the ink is controlled to within the range 8.5 to 9.5. This promotes stability in the ink, particularly where the ink may have to be stored over a period of time.

The invention is not limited to the embodiments hereinbefore described which may be varied in both construction and detail.

Claims (2)

1. A process for manufacturing a printing ink, comprising the steps: preparing selected powder pigments, taking a sample of each pigment, mixing said sample with a silicone wetting agent for forming a slurry, filtering the slurry, measuring the conductivity of the slurry for establishing the potassium chloride content of the pigment as an expression of the total salt content of the pigment, controlling the salt content of the pigment to a preset desirable range, weighing out a pre-desired amount of one or more of the selected powder pigments, delivering each selected powder pigment to a mixer, preparing a resin, weighing out a pre-desired quantity of resin, delivering the resin to the mixer, mixing the pigment with the resin in the mixer for a pre-desired time period for dispersing the pigment throughout the resin, forming an ink paste, ; delivering the ink paste to a mill, passing the ink paste through the mill, grinding the pigment into the resin in the mill, for producing an homogenous ink paste of a desired viscosity and reducing the pigment particles within the paste to a preset desirable size, - 8 combining selected additive materials with the paste for conditioning the paste and producing a printing ink of preset desirable characteristics .

2. A process as claimed in claim 1 wherein the process includes: preparing a set of base inks comprising a plurality of different coloured inks of a desired viscosity forming a spectrum of desired base ink colours, delivering each base ink to an associated holding tank, preparing a formulation for printing ink of a desired colour for forming a quantity of ink of the desired colour by combining two or more predetermined quantities of selected base inks of different colours, weighing a pre-desired amount of each selected base ink according to the formulation, delivering the selected base inks to a mixing tray, adding a preset amount of a drying agent to the mixing tray, mixing the selected base inks and the drying agent in the mixing tray for forming the printing ink of the desired colour, 15 6 delivering the coloured ink to a container. A process as claimed in claim 1 or 2 wherein the process includes the step of preparing the resin by combining preset amounts of two or more selected resins including a gel resin, controlling the amount of gel resin for controlling the viscosity of the ink to a preset desirable value. A process as claimed in claim 3 wherein the gel resin comprises between 30% and 60% by weight of the total resin. A process as claimed in any preceding claim wherein the process includes the step of controlling the pH of the printing ink to a pH of between 8.5 and 9.5. A process as claimed in claim 5 wherein the resin is a polyester resin and one of the additive materials comprises a cross-linking agent associated with the resin, the quantities of the resin and the cross-linking agent being in the ratio of 3:1 by weight in the ink. A process for manufacturing a printing ink substantially as hereinbefore described. A printing ink whenever produced according to the process as claimed in any preceding claim.